The present invention is directed to a pneumatic actuator for a gate valve for controlling exhaust gasses in a turbocharger, and more specifically to the bearing arrangement for the link mechanism associated with said actuator.
A conventional turbocharger for a vehicle engine is shown in FIG. 1 wherein the turbine 3 is driven by the exhaust gas flow from an exhaust manifold 2 through an exhaust passage 30. After the exhaust gas passes through the turbine 3, the exhaust gas is led to a catalytic converter 4. The turbine 3 drives a compressor 5 through shaft 31 supported in a housing 32 and the impeller of the compressor 5 compresses the air flow from passage 6 for delivery to an intake manifold 1. A gate valve 18 is provided in the passage 30 for diverting the exhaust gas flow from the turbine 3 in order to reduce the compressor speed. The gate valve 18 is moveable between the open and closed positions by means of a lever 17 which is pivoted at 16 with the opposite ends thereof being pivotally connected to the rod 14 of an actuator 9 by means of a pin 15 and the valve 18.
The actuator 9 is provided with a chamber 11 defined by a diaphragm 13 and a port 10 which communicates the chamber 11 with a passage 8 which is in communication with a port 7 in the passage 33 leading from the compressor 5 to the intake manifold 1. The diaphragm 13 is biased to the right, as viewed in FIG. 1, by means of a coil spring 12.
In such turbocharger systems, at higher engine speeds the exhaust gas flow is substantially increased so that the turbine 3 and compressor 5 will be driven at higher speeds. As a result, an excessive amount of compressed air is delivered to the intake manifold 1. As the air pressure in the passage 33 leading to the intake manifold 1 increases, the air pressure supplied to the chamber 11 of the actuator 9 through the passage 8 also increases. When the air pressure in the chamber 11 becomes larger than the biasing force of the spring 12, the diaphragm 13 will be moved to the left, as viewed in FIG. 1, and the rod 14 will be shifted to the left. The leftward movement of the rod 14 causes the lever 17 to rotate counterclockwise, as viewed in FIG. 1, and the gate valve 18 will be opened to permit the exhaust gas to bypass the turbine 3 to thereby decrease the rate of rotation of the compressor 5 to prevent overpressurization in the passage 33. Due to the pivoting action of the lever 17, the rod 14, which is pivotally connected to one end of the lever 17, does not reciprocate in a straight line, and, as a result, it is very difficult to provide a bearing in the actuator 9 for the rod 14. Therefore, vibrations transmitted from the engine and road are delivered to the diaphragm 13 through the rod 14, thereby adversely affecting the durability of the diaphragm 13.